UNIVERSITY    OF    CALIFORNIA 

COLLEGE     OF     AGRICULTURE 

AGRICULTURAL    EXPERIMENT    STATION 

BERKELEY,    CALIFORNIA 

CIRCULAR  No.  285 


SWEET  POTATO  PRODUCTION 
IN  CALIFORNIA 

BY 

J.  T.  EOSA 


FOKEWOBD 

The  sweet  potato  is  one  of  the  leading  truck  crops  of  the  United 
States,  but  at  the  present  time  it  is  only  of  minor  importance  in  Cali- 
fornia. In  1922,  the  year  of  heaviest  production,  there  was  grown  in 
the  United  States  1,117,000  acres  of  sweet  potatoes,  producing 
109,394,000  bushels.  The  crop  provided  approximately  55  pounds  of 
sweet  potatoes  per  capita  for  the  entire  population  of  the  United 
States.  In  the  same  year  the  acreage  of  sweet  potatoes  in  the  states 
west  of  the  Rocky  Mountains  was :  California  8000,  Arizona  2000  and 
New  Mexico  1000,  a  total  of  11,000  acres,  producing  1,292,000  bushels. 
Therefore,  for  the  seven  and  one-half  million  people  living  in  the  eight 
states  west  of  the  Rockies,  there  was  produced  in  this  district  only 
about  10  pounds  of  sweet  potatoes  per  capita.  This  small  production 
in  the  western  states  as  compared  with  that  of  the  country  as  a  whole 
has  resulted  in  a  low  per  capita  consumption  of  sweet  potatoes  and 
their  shipment  from  the  southern  and  middle  western  states  to  the 
Pacific  coast  markets.  Thus,  in  1923,  Los  Angeles  received  41  cars  of 
sweet  potatoes  from  Californian  points,  35  cars  from  Arkansas,  and  9 
cars  from  other  states.  The  sweet  potatoes  supplied  to  western  markets 
are  often  rather  poor  in  quality  and  inadequate  for  the  market 
demands.  The  retail  price,  moreover?  is  too  high  to  encourage  large 
consumption,  except  during  that  brief  portion  of  the  year  when  the 
crop  is  being  harvested  and  most  growers  are  hurrying  their  product 
to  market. 

On  the  other  hand,  returns  to  the  grower  have  not  always  been 
satisfactory  because  much  of  the  crop  is  sold  during  the  temporary 


Z  UNIVERSITY    OF    CALIFORNIA EXPERIMENT   STATION 

over-supply  of  the  markets  at  digging  time  in  the  fall.  The  1922  crop 
was  an  example  of  such  a  condition.  Prices  during  the  fall  were  so 
low  that  the  crop  of  some  fields  was  not  dug  at  all — yet  by  the  following 
February  the  wholesale  price  had  risen  to  5  cents  a  pound  for  the 
properly  cured  storage  house  product.  Adequate  storage  facilities 
would  make  it  possible  to  market  at  more  satisfactory  prices  many 
more  sweet  potatoes  than  are  now  grown  in  California.  Adequate 
storage  facilities  would  tend  to  eliminate  such  uneconomical  practices 
as  shipping  sweet  potatoes  from  Arkansas,  Tennessee,  and  other  dis- 
tant regions,  to  Pacific  coast  markets.  The  usual  seasonal  variation  in 
prices  of  sweet  potatoes  is  indicated  by  figures  1  and  2. 


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Fig.  1. — Seasonal  range  in  jobbing  prices  on  Jersey  and  Nancy  Hall  sweet 
potatoes  at  San  Francisco,  1922-1923. 


Factors  that  must  be  considered  if  yields,  production,  demand  and 
consumption  of  sweet  potatoes  are  to.be  increased,  are  disease  control, 
and  the  production  of  varieties  or  types  that  are  more  popular  with 
the  consumer.  Two  diseases  commonly  known  as  stem  rot  and  black 
rot  in  many  cases  are  destroying  10  to  50  per  cent  of  the  crop.  Both 
are  controllable  to  a  large  extent  by  well  proven  methods.  Varieties 
of  the  sweet,  moist-fleshed  type,  such  as  Nancy  Hall  and  Porto  Rico 
Yam,  are  not  only  more  productive  and  better  for  storage  than  the 
dry  meally  Jersey  type  now  so  generally  grown,  but  are  preferred  by 
many  consumers. 


Croc.  285] 


SWEET    POTATO   PRODUCTION    IN    CALIFORNIA 


It  is  the  purpose  of  this  circular  to  give  such  information  regarding 
sweet  potatoes  as  is  available  and  applicable  to  California  conditions, 
and  as  is  thought  necessary  to  increase  the  yield  and  the  market 
demand. 


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Fig.  2. — Seasonal  range,  jobbing  prices  on  sweet  potatoes, 
San  Francisco,  1923-1924. 


REQUIREMENTS  FOE  GEOWING  SWEET  POTATOES 

Soils. — Areas  for  commercial  sweet  potato  production  are  limited 
by  the  special  soil  requirements  for  growing  this  crop,  especially  under 
irrigated  conditions.  Generally,  light  sandy  loam  and  coarse  sandy 
soils  are  most  suitable.  Fresno  Sand  and  Oakley  Sand  are  the  soil 
types  most  used  for  sweet  potatoes.  The  fertility  necessary  as  com- 
pared with  that  required  by  other  crops  is  not  very  high.  Yet  some 
of  the  sandy  soils  on  which  sweet  potatoes  are  now  grown,  would 
probably  produce  larger  crops  if  organic  matter  and  commercial 
fertilizers  were  added.     The  physical  texture  of  the  soil  seems   to 


4  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

affect  both  the  form,  size,  and  smoothness  of  the  potatoes.  On  the 
heavier  soils,  the  top  growth  is  likely  to  be  so  excessive  as  to  retard 
maturity  and  cause  inconvenience  in  digging.  One  advantage  of  sandy 
soils  is  that  they  retain  less  of  the  irrigating  water  than  do  heavy 
soils.  The  plants  grown  on  sandy  soils,  therefore,  suffer  less  from 
excessive  moisture.  There  is  a  considerable  range  in  the  soil  adapta- 
tion of  different  varieties.  The  Jersey  type,  especially,  requires  sandy 
soils,  while  the  Nancy  Hall,  Porto  Rico,  and  some  of  the  large  white 
varieties  will  develop  satisfactorily  on  medium-heavy  loam  soils. 

Climate. — The  sweet  potato  requires  a  long  warm  growing  season. 
The  plants  are  very  sensitive  to  frost  and  therefore  cannot  be  set  in 
the  open  field  until  danger  of  frost  is  over.  Since  the  tops  are  also 
killed  by  the  first  heavy  frost  in  the  fall,  the  crop  should  be  dug  before 
or  soon  after  the  first  frost.  The  normal  development  of  the  plant  is 
retarded  by  cool  cloudy  weather  during  the  growing  season,  and  regions 
having  cold  nights  during  the  summer  are  not  favorable.  Hence, 
sweet  potatoes  are  grown  in  California  only  at  some  distance  from 
the  coast,  except  south  of  Los  Angeles. 

Moisture. — While  the  sweet  potato  plant  probably  uses  as  much 
water  as  any  other  crop  having  the  same  amount  of  foliage  and  grown 
under  the  same  conditions,  the  fact  remains  that  the  plant  is  not 
injured  seriously  by  rather  long  periods  of  drought.  This  has  led  to 
the  idea  that  sweet  potatoes  are  a  drought-resistant  crop.  Excellent 
crops  have  been  grown  in  the  Turlock  district,  on  sandy  land,  without 
irrigation,  but  such  soils  are  usually  sub-irrigated  to  some  extent  from 
nearby  canals.  Good  growth  and  yields  have  been  observed  where 
by  mid-summer  there  was  no  available  soil  moisture  nearer  than  20 
inches  to  2  feet  from  the  surface.  On  higher  lands  which  are  not  sub- 
irrigated,  regular  surface  irrigation  by  the  furrow  method  is  practiced. 

SWEET  POTATO  DISTEICTS 

The  larger  portion  of  the  sweet  potato  acreage  of  California  is 
located  in  Merced  and  Stanislaus  counties  in  the  extensive  area  of 
sandy  soils  adjoining  the  main  line  of  the  Southern  Pacific  railway. 
Both  soil  and  climate  are  very  favorable  for  maximum  yields  of  sweet 
potatoes  of  good  quality.  Smaller  sweet  potato  districts  are  located 
in  Los  Angeles  County,  in  the  San  Fernando  and  San  Gabriel  valleys, 
and  in  Orange  and  San  Diego  counties.  Sweet  potatoes  have  also 
been  grown  successfully  in  the  upper  part  of  the  Sacramento  Valley, 
at  Redding ;  in  Kern  County,  at  Bakersfield  and  Shafter ;  in  southwest 
Fresno  County,  and  to  a  small  extent  in  the  Imperial  Valley  near 
Yuma. 


ClRC.  285]  SWEET   POTATO   PRODUCTION    IN    CALIFORNIA 


GEOWING  THE  PLANTS 

Sweet  potatoes  are  usually  propagated  by  means  of  plants  produced 
from  small  potatoes  placed  in  a  hotbed,  with  proper  moisture  and 
temperature  conditions.  The  sweet  potato  itself  consists  of  a  root, 
originally  a  fibrous  feeding  root,  which  in  process  of  development  has 
thickened  for  a  greater  or  less  distance  from  the  central  stem.  On 
each  such  thickened  root,  or  potato,  are  found  four  rows  of  lateral 
fibrous  feeding  roots,  which  usually  disappear  before  the  crop  matures, 
so  that  only  the  slight  depressions  where  these  roots  were  attached  can 
be  seen.  From  the  neighborhood  of  these  root  scars,  adventitious  buds 
originate,  and  under  favorable  growing  conditions,  sprouts  are  formed. 
These  sprouts  have  an  independent  root  system  and  are  only  weakly 
connected  with  the  mother  potato,  from  which,  however,  they  derive 
most  of  their  food  up  to  transplanting  time.  The  sweet  potato  root 
has  no  true  rest  period,  for  the  sprouts  may  start  growing  at  any  time 
moisture  and  temperature  conditions  are  suitable.  This  often  occurs 
in  the  storage  house  in  the  early  part  of  the  storage  season,  also 
in  the  field  before  harvest,  when  the  partly  developed  roots  are 
separated  from  the  main  stem  by  diseases. 

The  potatoes  used  for  propagating  are  called  "seed"  or  "seed 
stock."  The  smaller  potatoes  ranging  from  one  to  two  inches  in 
diameter  are  most  suitable  for  this  purpose.  Larger  potatoes  may 
be  used,  but  they  are  more  expensive  and  do  not  produce  so  many 
plants  from  a  given  quantity  of  seed  stock.  Where  it  is  necessary 
to  use  large  potatoes,  the  yield  of  plants  can  be  increased  by  splitting 
the  potatoes  lengthwise,  and  bedding  with  the  flat  side  down.  The 
selection  of  sweet  potato  seed  is  discussed  in  detail  at  the  end  of  this 
circular.  Growers  in  the  Turlock  district  allow  about  400  pounds 
of  seed  for  each  acre  to  be  planted.  From  10,000  to  14,000  plants  to 
the  acre  are  required,  depending  on  the  distance  of  planting.  If  there 
is  no  disease,  the  seed  disinfected,  the  hotbed  properly  prepared  and 
carefully  handled,  200  pounds  of  seed  should  produce  enough  plants 
for  one  acre. 

Preparation  of  the  Hotbed. — The  bed  for  growing  sweet  potato 
plants  is  usually  heated  with  fresh  stable  manure.  It  should  be  located 
in  a  warm,  sunny,  well-drained  spot,  and  protected  from  north  winds, 
by  a  fence  or  windbreak.  A  trench  is  dug  6  to  8  feet  wide  and  15 
inches  deep,  and  as  long  as  necessary  to  accommodate  the  quantity  of 
seed  to  be  bedded.  When  plants  for  a  large  acreage  are  grown,  it  is 
best  to  arrange  the  plant  beds  in  short  sections  parallel  to  each  other. 
Several  days  before  the  sweet  potatoes  are  bedded,  the  trench  should 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT   STATION 


be  filled  with  fresh  heating  horse  manure  which  is  first  packed  by 
tramping",  then  covered  with  a  layer  of  3  to  4  inches  of  sandy  soil  or 
sand.  On  this  the  seed  potatoes  are  laid  about  one-half  inch  apart, 
when  the  bed  has  become  warm.  The  seed  should  be  covered  at  once 
to  a  depth  of  three  inches.  The  best  material  for  covering  is  clean 
sand,  preferably  taken  from  a  creek  bed  or  sand  pit  where  con- 
tamination by  sweet  potato  diseases  is  unlikely.  As  the  plants  or 
"sprouts"  can  obtain  all  the  necessary  nutriment  for  their  develop- 
ment from  the  mother  seed  potato,  there  is  no  need  for  a  fertile  soil 


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Fig.  3. — Fire-heated  hotbed.  Above  is  shown  cross-section  of  the  bed.  The 
flue-space  extends  the  entire  width  and  length  of  the  bed  and  is  covered  with 
rough  flooring.  Over  this  is  a  layer  of  tamped  soil  or  clay  from  3  to  6  inches 
deep,  above  which  is  the  sand  in  which  the  potatoes  are  bedded. 

Below  is  shown  a  side-section,  showing  arrangement  of  furnace  and  flue. 

in  the  plant  bed.  Furthermore,  sand  does  not  bake  and  crust  in  such 
a  way  as  to  prevent  the  sprouts  emerging,  as  heavier  soils  often  do. 
Also  the  formation  of  fibrous  roots  on  the  plants  is  much  more  extensive 
when  grown  in  sand,  than  in  heavier  soils.  The  last  is  an  important 
factor,  especially  with  varieties  such  as  the  Nancy  Hall,  which  form 
fibrous  roots  sparingly  and  are  therefore  more  difficult  to  transplant 
successfully.  Plants  grown  in  sand  are  also  pulled  up  more  easily 
and  with  less  damage  to  the  root  system.    Another  advantage  of  using 


Circ.  285] 


SWEET   POTATO   PRODUCTION    IN    CALIFORNIA 


clean  sand  in  the  preparation  of  the  sweet  potato  plant  bed  is  the 
avoidance  of  diseases,  especially  black  rot  and  stem  rot,  which  are 
likely  to  be  harbored  in  soils  taken  from  the  cultivated  fields,  or  which 
have  been  used  for  sweet  potato  beds  in  previous  years. 

Other  Types  of  Hotbeds. — Because  of  the  increasing  difficulty  of 
obtaining  sufficient  quantities  of  fresh  stable  manure  for  the  prepara- 
tion of  large  plant  beds  each  year,  other  methods  of  heating  the  beds 
may  have  to  be  resorted  to.  The  flue-heated  bed,  one  type  of  which 
is  shown  in  fig.  3,  is  well  suited  for  growing  sweet  potato  plants.    A  pit 


Fig.  4. — Top  view  of  fire-heated  hotbed,  concrete  construction.     (Courtesy 
New  Jersey  Experiment  Station.) 

is  located  at  one  end  of  the  bed.  Recessed  beneath  the  bed,  and  open- 
ing into  this  pit,  is  a  brick  furnace,  which  may  be  equipped  with  a 
grate  for  burning  coal  or  briquettes.  The  smoke,  fumes,  and  heat 
from  the  firebox  are  conducted  beneath  the  plant  bed,  either  through 
tile  flues  spaced  3  feet  apart  and  entering  a  chimney  at  the  far  end 
through  a  header ;  or  the  hotbed  may  have  a  tight  floor,  with  an  open 
space  beneath,  extending  for  its  entire  width  and  length  and  connected 
with  a  chimney  at  the  far  end.  Heaters  of  either  of  the  above  types 
may  accommodate  beds  8  to  12  feet  wide  and  40  feet  long.  For  larger 
beds,  it  may  be  more  economical  to  use  coils  of  pipe  for  steam  or  hot 
water  heating. 


8  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

In  the  cooler  sections,  sweet  potato  beds  are  enclosed  by  a  frame 
of  1  by  12  inch  boards  and  covered  with  glazed  sash  or  medium  weight 
unbleached  muslin  cloth,  water-proofed  by  treatment  with  hot  raw 
linseed  oil.  In  the  warmer  sections,  including  the  Turlock  district 
and  the  lower  San  Joaquin  Valley,  the  beds  are  seldom  enclosed,  but 
are  covered  with  board  shutters  3  to  4  feet  wide  and  slightly  longer 
than  the  bed  is  wide.  These  shutters  are  placed  on  the  surface  of  the 
beds  at  bedding  time,  to  retain  the  heat  in  the  bed.  m  After  the  bed  has 
once  warmed  up,  there  is  danger  of  over-heating,  and  the  shutters  are 
removed  from  time  to  time  to  regulate  the  temperature.  When  the 
plants  begin  to  push  through,  the  shutters  are  permanently  removed. 
A  thermometer  should  be  placed  near  the  center  of  the  hotbed,  and  the 
temperature  kept  around  80°  F.  until  the  sprouts  have  started. 

SEED  TEEATMENT 

One  of  the  most  important  steps  in  the  control  of  sweet  potato 
diseases  is  disinfection  of  the  seed  potatoes  before  bedding.  This  is 
especially  important  in  the  control  of  black  rot,  both  in  the  hotbed 
and  after  transplanting  to  the  field.  It  is  also  helpful  in  controlling 
other  diseases.  It  should  be  remembered  that  seed  treatment  is  only 
one  step  in  the  control  of  sweet  potato  diseases,  and  will  not  be  very 
effective  unless  the  other  precautions  for  disease  prevention — seed 
selection,  clean  hotbed  soils,  and  rotation  of  crops — are  also  observed. 
Seed  treatment  is  intended  to  destroy  the  disease  organisms  on  the 
surface  of  apparently  sound  healthy  seed.  Under  the  influence  of  the 
warmth  and  moisture  of  the  hotbed  these  organisms  grow  and  attack 
the  young  sprouts.  Many  of  the  plants  are  often  killed  in  this  way 
in  the  hotbed  before  transplanting,  and  many  others  are  infected 
and  die  later  in  the  field,  reducing  the  stand,  and  lessening  the  yield. 

The  standard  method  of  disinfecting  seed  sweet  potatoes  is  by 
dipping  the  seed  for  10  minutes  in  a  solution  made  up  at  the  rate  of 
one  ounce  of  corrosive  sublimate  (Bichloride  of  mercury  or  Mercuric 
chloride)  to  8  gallons  of  water.  The  corrosive  sublimate  should  be 
dissolved  beforehand  in  a  gallon  of  hot  water,  to  which  may  be  added 
one  pound  of  common  table  or  bulk  salt  to  hasten  the  process.  Fairly 
rapid  solution  can  be  obtained  even  in  cold  water  with  this  mixture 
of  the  corrosive  sublimate  and  table  salt. 

It  is  usually  convenient  to  dip  lots  of  from  60  to  75  pounds  of  seed 
at  a  time,  using  a  50-  or  60-gallon  wooden  barrel  containing  32  gallons 
of  the  solution.  Dipping  the  seed  for  longer  than  10  minutes  is  likely 
to  cause  injury. 


ClRC.  285]  SWEET   POTATO   PRODUCTION    IN    CALIFORNIA  9 

As  the  corrosive  sublimate  reacts  quickly  with  any  sort  of  metal, 
the  solution  should  be  prepared  and  handled  only  in  wooden,  stoneware, 
glass  or  enameled  containers.  As  it  is  also  deadly  poison  to  all  animal 
life  the  powder  and  the  solution  must  be  kept  out  of  reach  of  children 
and  stock. 

The  solution  of  corrosive  sublimate  is  weakened  by  dipping  the 
seed  potatoes.  Gunny  sacks  should  not  be  used  for  containers  in  dip- 
ping the  seed  because  the  jute  fibre  from  which  they  are  made  absorbs 
large  amounts  of  the  chemical  from  the  solution.  Wooden  baskets  or 
cotton  sacks  may  .be  used,  or  the  seed  may  be  dumped  into  the  solution 
loose.  The  last  is  the  best  practice  if  the  barrel  or  dipping  vat  is 
located  on  an  elevated  platform,  and  is  provided  with  a  large  drain 
plug  so  that  the  solution  can  be  promptly  drained  off  into  another 
barrel  at  the  end  of  each  treatment. 

To  keep  the  solution  up  to  the  original  strength,  a  small  amount  of 
corrosive  sublimate  should  be  added  occasionally.  It  has  been  found 
by  experiments  that  the  addition  of  one-half  ounce  for  every  100 
pounds  of  seed  treated,  together  with  enough  water  to  restore  the 
original  volume,  will  keep  the  strength  of  the  solution  about  constant. 
If  the  solution  is  used  over  four  times  without  addition  of  more  cor- 
rosive sublimate  it  becomes  so  weak  that  the  treatment  is  not  effective. 
If  a  stock  solution  of  4  ounces  to  the  gallon  has  been  prepared,  one  pint 
of  this  should  be  added  for  every  100  pounds  of  seed  dipped. 

The  seed  potatoes,  upon  removal  from  the  solution,  should  be 
allowed  to  drain  a  minute  or  two,  then  placed  directly  in  the  hotbed, 
without  rinsing. 

TRANSPLANTING 

The  transplanting  of  the  plants  from  the  hotbed  to  the  field  should 
begin  as  soon  as  danger  of  frost  is  over,  and  the  preparation  of  the 
hotbed  should  consequently  be  timed  so  that  the  first  crop  of  plants  is 
ready  for  transplanting  about  the  time  the  weather  becomes  warm 
enough  for  field  setting.  In  the  Los  Angeles  district,  transplanting 
usually  begins  about  April  1  and  continues  until  the  first  part  of  June. 
In  the  San  Joaquin  Valley,  transplanting  begins  the  latter  part  of 
April  and  continues  until  late  in  June.  Objections  to  late  planting 
are  that  it  is  difficult  to  secure  a  good  stand  because  of  the  heat,  and 
that  the  shorter  growing  season  reduces  the  yield.  It  is  the  general 
experience  of  growers  in  California  that  the  earlier  transplantings 
produce  the  larger  crop.  Some  experiments  in  Kern  County,  con- 
ducted by  W.  B.  Camp  in  1923,  strikingly  demonstrate  the  decrease 
in  yield  from  late  plantings.  The  test  included  Southern  Queen,  Nancy 


10  UNIVERSITY   OF    CALIFORNIA EXPERIMENT   STATION 

Hall,  Dooley,  Porto  Kico,  and  Big  Stem  Jersey,  the  results  with  all 
being  similar  to  those  given  below  for  the  Jersey  variety. 

Date  Transplanted  Besults — Dug  October  21 

May  21  Good  yield.     Large  uniform  potatoes,  nearly  all  marketable. 

June  9  Fair  yield,  many  medium  size  potatoes,  30  per  cent  small. 

June  25  Light  yield,  nearly  all  small  potatoes. 

July  11  Light  yield,  all  small  potatoes. 

In  pulling  the  plants  for  transplanting,  the  mother  or  "seed 
potato"  is  held  in  place  with  one  hand  and  the  plants  are  pulled  up 
with  the  other.  Plants  more  than  10  inches  high  should  be  pruned 
by  cutting  off  the  tops  of  the  bundles  of  plants  with  a  large  knife. 
After  pulling,  the  plants  should  be  kept  out  of  the  sun  until  trans- 
planted. The  roots  especially  should  be  kept  from  drying  out.  Sweet 
potato  plants  may  be  held  for  several  days  after  pulling  or  may  be 
shipped  long  distances,  if  the  roots  are  kept  slightly  moist,  by  wrapping 
in  moistened  newspaper.  The  tops  must  be  kept  dry,  otherwise  slimy 
decay  takes  place  within  a  day  or  two. 

Most  of  the  commercial  acreage  of  sweet  potatoes  is  set  with  horse- 
drawn  transplanting  machines,  of  which  there  are  several  types  on  the 
market.  These  machines  are  equipped  with  a  tank  and  an  automatic 
device  which  discharges  a  small  amount  of  water  at  the  roots  of  each 
plant  as  it  is  set.  Even  though  the  soil  seems  moist  at  transplanting 
time,  it  is  best  to  use  the  watering  attachment.  On  very  sandy  soils, 
which  dry  out  quickly,  and  when  transplanting  late  in  spring,  it  is  best 
to  give  a  row  irrigation  within  a  day  or  two  to  moisten  the  ridges  and 
give  the  young  plants  a  favorable  start  before  they  have  become  dry. 

Propagation  by  Vine  Cuttings. — In  the  southern  states  it  is  custom- 
ary to  grow  a  late  crop  from  vine  cuttings  or  "slips"  taken  from  the 
tops  of  the  early  crop,  which  is  always  grown  from  plants  propagated 
in  hotbeds.  The  cuttings  of  the  sweet  potato  take  root  readily  when 
severed  from  the  parent  plant  and  transplanted  to  a  new  location 
under  favorable  conditions.  Koots  form  very  quickly  from  the  nodes. 
The  cuttings  may  be  from  10  to  30  inches  long,  but  the  shorter 
cuttings  are  much  more  conveniently  handled  when  transplanted  by 
machine.  Propagation  by  cuttings  does  not  seem  to  be  generally 
advisable  in  California  because  of  the  difficulty  of  getting  a  stand  in 
mid-summer,  and  the  small  yield  produced  by  late  plantings.  Propa- 
gating in  this  way,  however,  may  be  desirable  for  one  reason :  namely, 
the  production  of  potatoes  free  from  disease  especially  for  seed  pur- 
poses. One  of  the  worst  diseases,  stem  rot,  is  spread  from  year  to  year 
within  the  seed  potatoes.     The  disease  works  within  the  stem  of  the 


ClRC.  285]  SWEET   POTATO   PRODUCTION    IN    CALIFORNIA  11 

plant,  from  the  root  upward.  However,  cuttings  taken  from  the  tips 
of  vines  that  appear  to  be  healthy,  early  in  the  season,  are  very  likely 
to  be  free  of  disease,  and  if  transplanted  to  a  field  where  the  soil  is  also 
free  from  sweet  potato  diseases  will  produce  healthy  potatoes.  This 
method  then  results  in  production  of  seed  that  is  nearly  disease-free, 
and  may  be  expected  to  produce  healthy  plants  if  bedded  under  proper 
conditions  the  next  spring.  "Slip  seed"  grown  on  nematode-free  soil 
is  also  the  only  way  to  make  certain  of  nematode-free  seed. 

This  practice  is  known  in  the  South  as  "slip  seeding"  and  is  of 
importance  in  controlling  disease,  if  other  precautions  are  also 
observed.  A  very  satisfactory  crop  of  seed  was  grown  at  Delhi. 
California,  in  1924,  by  this  method. 

CULTUEAL  PEACTICES 

The  exact  details  of  culture  for  sweet  potatoes  vary  in  different 
localities.  A  few  general  suggestions,  however,  may  be  useful  to  the 
prospective  grower  who  has  had  no  experience  with  this  crop. 

Sweet  potatoes  are  nearly  always  planted  on  ridges  from  8  to  15 
inches  high,  the  lower  ridges  being  generally  preferred.  Kidge-culture 
provides  more  favorable  conditions  for  the  development  of  the  roots, 
facilitates  row  irrigation  and  reduces  the  labor  of  harvesting  as  com- 
pared to  flat  culture.  The  rows  are  generally  marked  off  3  feet  apart, 
and  the  ridges  formed  with  a  lister.  The  riding  disc  cultivator  can 
also  be  used  to  form  ridges  after  removing  all  but  the  two  inner  discs 
and  setting  these  at  the  proper  angle  to  form  a  ridge  between  them. 
The  tops  of  the  ridges  are  smoothed  slightly  with  a  plank  drag  before 
setting  plants,  if  a  transplanting  machine  is  used. 

The  spacing  of  plants  in  the  row  should  be  varied  to  suit  conditions. 
Varieties  that  tend  to  make  excessively  large  potatoes,  especially  the 
Nancy  Hall,  should  be  set  much  closer  than  varieties  that  tend  to  pro- 
duce a  larger  number  of  medium-sized  potatoes,  such  as  the  various 
strains  of  the  Jersey  type.  On  the  more  fertile  soils  all  varieties  should 
be  spaced  closer  than  on  poorer  soils.  The  average  distance  between 
plants  in  the  row  is  15  inches.  This  may  be  shortened  to  10  inches,  or 
lengthened  to  18  inches,  according  to  the  variety  and  soil  fertility. 

When  the  young  plants  begin  to  send  out  runners,  it  is  necessary 
to  turn  these  so  that  they  will  grow  along  the  ridge  and  not  interfere 
with  cultivation  between  the  rows.  This  vine  turning  is  usually  per- 
formed by  hand,  but  some  of  the  growers  equip  their  cultivators  with 
rods  to  lift  the  vines  out  of  the  way.  If  the  tips  of  the  vines  are 
covered  with  soil  during  cultivation  they  are  likely  to  take  root  and 


12  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

form  small  potatoes  which  detract  from  the  development  of  the  potatoes 
in  the  main  hill.  Eventually  the  vines  cover  the  space  between  the 
rows  and  cultivation  is  discontinued,  though  irrigation  may  be 
continued  as  late  as  September  1  on  late  plantings. 

Most  of  the  sweet  potatoes  in  California  have  hitherto  been  grown 
on  sub-irrigated  land  in  the  Stanislaus-Merced  district  with  the  water 
table  4  to  5  feet  below  the  surface  during  the  growing  season.  With  the 
lining  of  the  canals  to  prevent  seepage  and  the  pumping  being  carried 
on  in  some  districts  to  lower  the  water  table,  it  will  probably  become 
necessary  to  resort  to  surface  irrigation.  The  crop  can  be  grown  very 
successfully  with  surface  irrigation  (by  the  furrow  method)  but  the 
cost  is  greater  than  under  sub-irrigated  conditions.  Where  sweet 
potatoes  are  to  be  surface-irrigated,  the  land  should  be  carefully  graded 
and  the  water  handled  so  as  to  get  as  even  a  distribution  as  possible. 
During  the  dry  season  of  1924  many  fields  received  emergency  irriga- 
tions and  it  was  found  that  in  those  portions  of  the  fields  where  too 
much  water  was  received  the  potatoes  were  over-sized  and  rough,  and 
many  of  them  cracked. 

Even  more  important  is  the  relation  of  soil  moisture  to  disease. 
During  1924,  the  portions  of  the  fields  that  were  rather  dry  or  that 
received  only  a  moderate  amount  of  water  were  fairly  free  from  the 
black  rot  disease.  In  the  lower  and  excessively  moist  portions  of  the 
fields  a  very  large  proportion  of  the  potatoes  were  affected  with  black 
rot.  Careful  and  uniform  distributions  of  water  will  do  much  to 
lessen  the  losses  caused  by  this  disease. 

On  sub-irrigated  land  two  surface  irrigations  are  usually  given 
shortly  after  transplanting.  On  the  higher  lands,  about  seven  irriga- 
tions during  the  growing  season  are  required. 

HARVESTING 

The  time  of  harvesting  depends  on  market  conditions  and  the 
maturity  of  the  crop.  Sweet  potatoes  planted  out  in  May  will  con- 
tinue growing  until  the  tops  are  frosted  in  November.  The  rate  of 
growth  of  the  potatoes  themselves  has  not  been  determined  for  Cali- 
fornia conditions,  but  the  increase  in  yield  for  the  last  few  weeks  of 
growth  is  probably  not  very  great  at  least  for  early  planted  potatoes. 
On  the  other  hand,  there  is  a  period  in  the  middle  of  the  season  when 
the  increase  in  size  of  the  potatoes  is  very  rapid. 

Harvesting  begins  in  August  in  central  California,  and  slightly 
earlier  in  southern  California.  The  first  sweet  potatoes  from  Imperial 
Valley,  reach  market  about  July  15.     Even  the  earliest  plantings  are 


Cmc.  285] 


SWEET   POTATO   PRODUCTION    IN    CALIFORNIA 


13 


not  nearly  full  grown  when  harvesting  begins,  but  the  high  price 
received  for  the  earliest  potatoes  compensates  for  the  smaller  yield. 
Harvesting  increases  in  volume  through  September  and  October.  Prac- 
tically all  of  the  sweet  potatoes  dug  before  the  middle  of  October  are 
sold  on  local  markets  or  shipped  at  once.  Those  intended  for  storage 
are  harvested  from  the  middle  of  October  until  after  the  tops  have 
been  frosted.  The  effect  of  the  freezing  of  the  tops  on  the  quality  of 
the  roots  is  a  much  disputed  question,  though  it  is  generally  believed 
that  unless  the  tops  are  cut  off  the  day  after  the  first  killing  frost  the 


Fig.  5. — Vine  cutter,  drawn  by  one  horse,  used  in  stripping  sweet  potato 
vines  in  Virginia.     (Courtesy  Virignia  Truck  Experiment  Station.) 


potatoes  will  not  keep  well  in  storage.  Certainly  the  effect  of  tem- 
perature low  enough  to  freeze  the  tips  of  the  potatoes  themselves,  either 
before  or  after  digging,  is  disastrous. 

In  harvesting,  the  first  step  is  to  dispose  of  the  tops.  Most  of  the 
California  growers  now  do  this  by  hand,  using  long  curved  knives  to 
cut  them  from  the  central  stem.  They  are  then  removed  and  piled  in 
convenient  places  to  be  used  later  in  covering  the  heaps  of  potatoes. 
Recently  the  value  of  the  tops  as  stock  feed  has  been  realized,  and 
many  of  them  are  taken  from  the  fields  by  the  dairymen  for  feeding  to 
their  cattle.  The  tops  may  also  be  clipped  from  the  main  stem  with  a 
hoe,  and  left  between  the  rows  so  that  they  will  be  buried  in  plowing 
out  the  potatoes.  In  some  eastern  districts  the  slow  laborious  task  of 
cutting  the  tops  by  hand  is  avoided  by  the  use  of  a  horse-drawn  "vine 
cutter, ' '  such  as  that  shown  in  fig.  5. 


14  UNIVERSITY    OF    CALIFORNIA EXPERIMENT   STATION 

After  the  tops  are  cut  and  removed  from  the  ridges,  the  roots  are 
plowed  out.  A  14-inch  mold-board  plow  may  be  used  for  this  purpose. 
Most  growers,  however,  have  plows  with  specially  adapted  mold-boards 
for  this  work.  One  grower,  Mr.  J.  B.  Steele  of  Baldwin  Park,  Cali- 
fornia, has  adapted  an  old  Irish  potato  digger  for  harvesting  sweet 
potatoes,  by  removing  the  elevator  apron  and  welding  on  an  extra  wide 
and  heavy  point.  The  ordinary  potato  digger  has  not  proved  success- 
ful with  sweet  potatoes  because  of  the  large  amount  of  power  required 
and  the  excessive  bruising  of  the  potatoes.  After  plowing  out,  the 
crop  should  be  gathered  promptly.  In  the  San  Joaquin  Valley  the 
practice  is  to  leave  the  potatoes  attached  to  the  central  stem  and  gather 
the  crop  into  large  piles  at  convenient  intervals  through  the  field. 
These  piles  are  covered  with  sweet  potato  tops  to  protect  them  from  the 
sun  and  from  light  frosts  that  are  likely  to  occur  late  in  the  fall.  As  a 
rule,  the  potatoes  are  sorted  from  the  piles  and  packed  in  shipping 
crates  the  day  they  are  dug.  This  practice  is  probably  the  most  con- 
venient and  economical  where  the  potatoes  are  being  dug  for  immediate 
shipment.  However,  the  covered  piles  may  be  left  in  the  field  for 
several  days.  The  over-sized,  the  cracked,  the  small  or  seed-sized,  the 
stringy  potatoes  and  the  stem  are  left  on  the  ground  to  be  gathered  up 
later.  This  practice  makes  it  impossible  to  select  healthy  seed — a 
thing  that  is  best  done  in  the  field  at  the  time  of  digging.  When  the 
potatoes  have  been  snapped  from  the  stems,  it  is  impossible  to  tell 
which  have  come  from  healthy  plants,  and  which  from  diseased  plants. 
The  safest  plan  is  to  inspect  the  individual  hills  immediately  after 
plowing  out,  choosing  those  which  show  potatoes  of  desirable  type,  and 
which  prove  to  be  healthy  upon  splitting  the  central  stem.  The  smaller 
sized  potatoes,  still  attached  to  the  stem,  may  then  be  gathered  and 
saved  for  seed  purposes.  A  few  careful  growers  have  been  successful 
in  selecting  healthy  seed  from  the  piles,  however,  by  inspecting  the 
stem  of  each  intact  hill  and  laying  aside  the  " seed-size"  potatoes  at 
the  time  the  No.  1  potatoes  are  packed. 

In  harvesting  sweet  potatoes  it  is  essential  to  avoid  all  rough 
handling  that  tends  to  bruise  them.  The  skin  is  very  tender  when  the 
potatoes  are  dug,  and  it  is  easily  broken  or  rubbed  off.  Where  the 
flesh  is  exposed  in  this  way,  the  molds  that  cause  rotting  are  likely  to 
gain  entrance  and  even  if  rot  does  not  occur,  a  sunken  discolored  spot 
is  caused  that  injures  the  appearance.  All  unnecessary  handling 
should  be  avoided  especially  for  potatoes  that  are  to  go  into  storage. 
Storage  stock  should  be  placed  in  lug  boxes  without  piling,  hauled 
directly  to  the  storage  house,  and  emptied  into  storage  bins  at  once. 


ClRC.  285]  SWEET   POTATO   PRODUCTION    IN    CALIFORNIA  15 


PACKING 

For  many  years,  the  standard  container  for  California-grown  sweet 
potatoes  was  the  100-pound  crate.  Experience  has  shown,  however, 
that  this  is  too  large  and  heavy  for  the  best  results  in  shipping,  and 
in  recent  years  most  of  the  crop  has  been  packed  in  "Special"  or 
"three-quarter"  crates  which  hold  75  to  80  pounds  as  packed  in  the 
field.  The  inside  dimensions  of  this  crate  are  9%  by  14  by  22%  inches. 
In  packing  the  crate  is  first  nearly  filled  and  then  a  top  layer  of 
uniform-sized  potatoes  is  carefully  arranged  so  as  to  give  a  good  bulge 
to  the  cover  when  nailed  on.  The  pressure  from  this  bulge  holds  the 
potatoes  firm,  thus  preventing  movement  in  the  crate,  and  lessening  the 
injury  to  the  appearance  of  the  potatoes  in  a  slack  pack. 

The  U.  S.  Standard  Grade  for  No.  1  sweet  potatoes  calls  for  potatoes 
not  less  than  1%  inches  and  not  over  3%  inches  in  diameter.  These 
size  requirements  are  rather  carefully  observed  by  California  growers. 
The  over-sized  "Jumbo"  potatoes  as  well  as  the  cracked,  cut,  or  other- 
wise imperfect  potatoes  are  usually  not  marketable,  except  as  stock 
feed.  It  is  estimated  that  when  barley  is  worth  $50  a  ton,  sweet 
potatoes  are  worth  $15  as  feed  for  dairy  cattle.  The  sizes  below  No.  1 
grade  are  utilized  for  canner  stock  and  for  seed.  For  canning,  long 
potatoes  from  %  to  1%  inches  in  diameter  are  demanded.  Somewhat 
smaller  potatoes  serve  as  well  or  better  for  seed.  The  "strings"  also 
have  some  value  as  feed  for  hogs. 

VAEIETIES 

Of  the  many  varieties  of  sweet  potatoes  grown  in  the  United  States, 
only  a  few  are  important  in  California.  From  the  marketing  stand- 
point, this  is  fortunate,  for  when  a  district  specializes  on  one  or  two 
varieties  of  a  crop  it  is  easier  to  put  out  a  standardized  product  and  to 
build  up  an  established  reputation  for  it.  Still,  the  leading  varieties 
differ  enough  in  their  adaptability  to  different  soils  and  localities, 
suitability  for  market  purposes  and  other  characteristics,  to  justify  the 
grower  in  considering  carefully  the  varietal  question.  Below  are 
discussed  some  of  the  main  points  connected  with  varieties  now  grown 
or  likely  to  be  grown  in  California. 

The  Jersey  Type. — There  are  several  distinct  strains  of  this  general 
type,  which  together  comprise  most  of  the  commercial  acreage.  One 
strain  has  been  grown  in  this  state  for  many  years,  and  is  generally 
spoken  of  as  the  "Old  California."  It  appears  to  be  distinct  from 
any  of  the  Eastern  strains.    The  potatoes  are  long  and  slender,  there 


16  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION 

are  a  large  number  to  the  plant,  and  under  unfavorable  growing  con- 
ditions many  of  them  do  not  reach  sufficient  thickness  for  the  market 
grade.  Generally,  this  strain  produces  a  larger  proportion  of  canner 
and  seed  stock  than  any  other  variety  or  strain  grown.  Its  vines  are 
rather  slender  with  small  leaves  of  variable  type,  some  being  narrow 
and  pointed,  some  distinctly  forked  or  three-lobed,  and  others  broadly 
triangular.  Another  strain,  grown  extensively  in  recent  years,  is 
generally  referred  to  as  the  "New  Jersey"  strain,  seed  having  been 
imported  from  that  state  about  1921.  This  is  the  same  as  the  Eastern 
variety,  Little  Stem,  or  Up  River.  It  can  scarcely  be  distinguished 
from  the  California  strain  by  the  appearance  of  the  leaves  or  runners ; 
the  potatoes,  however,  are  much  shorter  and  thicker,  more  chunky  or 
short-spindle  shaped  than  the  California.  This  strain  has  become 
very  popular,  as  it  produces  a  large  yield  with  a  high  percentage  of 
No.  1  potatoes.  A  third  strain  is  the  Bed  Jersey,  quite  similar  to  the 
New  Jersey  strain  in  every  respect  except  the  intense  red  color  of  the 
skin.  It  has  no  special  qualities  to  commend  it  and  is  not  in  demand  on 
the  markets. 

The  Jersey  strains  in  general  produce  well  on  very  sandy  soil,  but 
perhaps  are  the  least  adapted  of  all  varieties,  to  the  heavier  soils.  This 
type  of  sweet  potato  has  a  dry  mealy  flesh,  which  is  preferred  by  some 
people.  At  present  it  is  the  most  popular  variety  for  summer  and 
fall  use  on  the  Pacific  coast  markets,  but  generally  sells  at  a  lower 
price  than  other  varieties  during  the  winter.  The  various  strains  of 
this  type  are  rather  early  in  maturing.  The  small  light  growth  of  top 
and  the  fact  that  potatoes  adhere  to  the  central  stem  more  strongly 
than  other  varieties,  are  advantages  in  harvesting.  In  storage-quality, 
the  Jersey  type  is  decidedly  inferior  to  other  varieties  even  under  the 
best  conditions,  the  potatoes  usually  beginning  to  shrivel  at  the  stem 
end  about  a  month  after  being  placed  in  storage.  This  defect  in  the 
Jersey  type  is  more  noticeable  in  California  than  in  the  East.  Because 
of  its  poor  keeping  quality  and  the  market  preference  for  other  sorts 
in  winter,  it  is  not  advisable  to  store  the  Jersey  type  in  commercial 
quantities  for  more  than  a  few  weeks. 

Nancy  Hall. — This  variety  has  recently  been  grown  in  California  in 
commercial  quantities  and  is  justly  increasing  in  favor.  The  potatoes 
are  medium-long,  spindle-shaped,  tapering  at  both  ends,  smooth  and 
uniform  when  grown  under  favorable  conditions.  The  skin  is  light 
pink  of  uneven  density.  The  flesh  is  pink  while  raw,  becoming  golden 
yellow  and  very  sweet  and  juicy  when  cooked.  Many  prefer  this  type 
when  they  once  become  acquainted  with  it.  Varieties  like  the  Nancy 
Hall  having  moist  sweet  flesh  are  often  spoken  of  as  "Yams"  though 


ClRC.  285]  SWEET   POTATO   PRODUCTION    IN    CALIFORNIA  17 

the  true  Yam  is  a  tropical  plant  belonging  to  another  botanical  family, 
and  is  not  grown  in  the  United  States.  The  Xancy  Hall  is  early  and 
very  productive.  It  is  one  of  the  best  keeping  varieties,  and  therefore 
well  suited  for  storage.  While  best  adapted  to  the  sandy  soils,  this 
variety  thrives  well  enough  on  moderately  heavy  soils  to  make  a  satis- 
factory crop  for  home  use.  On  account  of  the  rapid  early  growth  of 
the  potatoes  and  of  their  tendency  to  grow  too  large,  this  variety  can 
be  dug  for  the  extra  early  crop  when  only  half  grown,  yet  produce 
satisfactory  yields.  Objections  to  this  variety  are :  its  tendency  to 
grow  potatoes  that  are  too  large  or  rough ;  susceptibility  to  Stem  Rot 
disease ;  and  difficulty  in  obtaining  a  good  stand  of  plants  in  the  field, 
on  account  of  small  number  of  roots  formed  by  the  sprouts  before 
transplanting  from  the  hotbed.  The  tendency  to  over-sized  roots  can 
be  corrected  by  setting  the  plants  close  in  the  row.  Spacing  the  plants 
as  close  as  6  inches  in  the  row  has  been  found  to  give  maximum  yields 
on  moist  fertile  soils. 

Porto  Rico. — This  variety  is  of  somewhat  the  same  general  type 
as  the  Nancy  Hall;  but  is  considered  superior  in  some  respects.  The 
potatoes  are  of  a  deep  coppery  red  and  have  a  deep  pink  flesh,  which  is 
richly  colored  and  very  sweet  and  juicy  when  cooked.  The  potatoes 
are  rather  irregular,  though  most  of  them  are  spindle-shaped,  and 
of  medium  length.  This  variety  has  been  very  successfully  grown  in 
the  Los  Angeles  district  for  several  years  and  in  1924  several  small 
patches  grown  at  Turlock  and  Delhi  proved  its  adaptability  to  the 
San  Joaquin  Valley.  Though  this  variety  is  practically  unknown  on 
the  markets  of  northern  California  and  the  Northwestern  states,  its 
fine  qualities  will  soon  render  it  popular  in  these  sections.  It  is  not 
particularly  early,  but  is  well  suited  for  the  main  fall  shipping  crop 
and  for  winter  storage. 

Southern  Queen, — This  is  a  large  coarse-growing  variety,  having 
white  skin  and  cream-colored  flesh.  Though  not  in  demand  on  the 
markets,  because  of  the  white  color,  it  is  of  fairly  good  eating  quality 
after  it  has  been  in  storage  for  several  months.  This  variety  is  hardly 
grown  at  all  in  California.  It  is  known  in  the  Turlock  district  as 
the  "Tennessee." 

STOEAGE 

The  sweet  potato  is  commonly  regarded  as  a  difficult  crop  to  store 
over  winter,  because  of  its  sensitiveness  to  cold  and  susceptibility  to 
rots  caused  by  fungi  when  the  storage  conditions  are  defective.  How- 
ever, during  the  past  ten  years  very  satisfactory  and  dependable 
methods  for  sweet  potato  storage  have  been  worked  out,  largely  by  the 
U.  S.  Department  of  Agriculture,  and  thousands  of  the  modern  storage 


18  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION 

houses  have  been  erected  in  the  southern  and  eastern  states.  California 
growers  have  been  very  slow  to  provide  suitable  storage  facilities  for 
sweet  potatoes.  There  is  only  one  large  storage  house  and  two  small 
houses  of  more  or  less  modern  type  in  the  state.  On  account  of  the  mild 
climate,  California  growers  have  been  fairly  successful  in  storing  sweet 
potatoes  in  cellars  in  some  years.  However,  conditions  in  these  cellars 
are  seldom  well  regulated  and  the  losses  by  decay  and  shrinkage  are 
generally  very  heavy,  a  total  loss  being  a  common  occurrence  in  cold 
or  wet  seasons.  The  inferior  quality  of  cellar  stock  as  compared  to 
1 '  cured, "  or  the  storage  house  stock,  is  reflected  in  the  much  lower 
prices  paid  for  the  former.  Data  from  the  San  Francisco  market 
reports  bear  out  this  statement. 

The  great  advantage  of  storing  sweet  potatoes  is  that  it  greatly 
extends  the  marketing  season  and  the  period  for  consuming  the  crop. 
Instead  of  forcing  the  entire  crop  onto  the  market  during  the  digging 
season,  from  August  to  November,  a  large  part  may  be  held  in  storage 
for  marketing  during  the  winter  and  early  spring.  Sweet  potatoes  can 
easily  be  kept  as  late  as  May  1.  Thus  the  length  of  the  sweet  potato 
season  may  be  doubled.  Unlike  many  vegetables,  sweet  potato  con- 
sumption is  not  seasonal.  If  available,  they  are  used  as  extensively  in 
winter  as  in  autumn.  Development  of  more  and  better  storage  facili- 
ties will  provide  an  outlet  for  much  larger  crops  of  sweet  potatoes 
than  have  ever  been  grown  in  California. 

The  sweet  potato  requires  a  warm,  dry,  well  ventilated  storage  place 
if  it  is  to  be  kept  through  the  winter  with  minimum  loss  from  shrinkage 
and  decay.  An  important  factor  is  a  preliminary  "curing"  or  sweat- 
ing process,  given  for  the  first  10  to  14  days  after  the  potatoes  go  into 
storage.  During  this  period  the  temperature  should  be  held  at  80° 
to  85°  F.,  and  the  ventilators  kept  open  so  that  excess  moisture  can 
pass  off  from  the  potatoes  freely.  Some  chemical  changes  occur  in 
the  potatoes  themselves  during  this  curing  process :  the  skins  become 
tougher  and  thicker,  and  the  cut  and  bruised  places  seal  over  so  that 
rot-producing  fungi  cannot  gain  entrance.  After  curing,  the  storage 
rooms  should  be  held  at  50°  to  55°  F.,  with  the  ventilators  opened  or 
closed  according  to  temperature  and  moisture  conditions  outdoors.  The 
necessary  conditions  for  curing  and  holding  sweet  potatoes  through 
the  winter  can  best  be  supplied  in  specially  constructed  sweet  potato 
houses.  These  houses  do  not  have  to  be  so  substantially  constructed 
in  California  as  they  do  in  eastern  states,  and  need  not  be  expensive. 
Persons  interested  in  commercial  storage  of  sweet  potatoes  are  advised 
to  secure  Farmers'  Bulletin  No.  970  from  the  U.  S.  Department  of 
Agriculture,  Washington,  D.  C. 


Cmc.  285] 


SWEET   POTATO   PRODUCTION    IN    CALIFORNIA 


19 


Fig.  6. — Showing  dead  plants  and  missing  places  in  sweet  potato  field,  just 
before  harvest.    Due  to  black  rot,  chiefly. 


Fig.  7. — Healthy  field  of  sweet  potatoes  with  practically  no  missing  places. 
Seed  were  carefully  selected  and  dipped  in  Corrosive  Sublimate  solution.  Nancy 
Hall  variety  on  left,  Jerseys  on  right.    A.  R.  Vierra,  Turlock,  California. 


20  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


DISEASES 

The  sweet  potato  is  subject  to  several  destructive  diseases,  affecting 
both  the  plant  and  the  potato,  and  to  some  diseases  which  attack  the 
potato  only.  These  diseases  have  been  increasing  in  severity  in  recent 
years.  Some  of  them  are  prevalent  at  the  present  time,  and  are  the 
cause  of  great  loss  to  the  growers  who  often  are  not  aware  of  them. 
The  control  of  disease  is  the  chief  problem  now  confronting  California 
growers,  from  the  standpoint  of  production. 

During  the  summer  of  1923  and  1924  many  fields  in  the  main 
sweet  potato  districts  were  visited  by  the  writer.  In  most  cases  some 
disease  was  present,  and  in  some  fields  40  to  50  per  cent  of  the  plants 
were  dead  or  dying  of  disease.  There  can  be  little  profit  with  such  a 
large  reduction  in  the  stand.  It  costs  as  much  to  plant,  cultivate,  and 
irrigate  a  field  with  only  half  a  stand  of  plants  as  with  a  full  stand. 
Losses  of  plants  of  only  10  or  15  per  cent,  which  may  not  even  be 
noticed  by  the  grower,  will  reduce  the  yield  in  nearly  the  same  ratio, 
which  in  years  of  low  prices  may  entirely  prevent  all  profit.  Losses 
of  plants  just  after  transplanting  are  often  attributed  by  growers  to 
causes  other  than  disease,  while  death  of  plants  during  the  growing 
season  often  passes  unnoticed.  The  chief  diseases  are  so  widely  spread 
and  may  cause  such  heavy  losses  that  the  simple  specific  measures  for 
preventing  them  should  always  be  followed,  whether  or  not  the  growers 
know  them  to  be  present. 

The  two  diseases  which  cause  most  loss  in  California,  commonly 
known  as  stem  rot  and  black  rot,  are  prevalent  in  other  parts  of  the 
country  also,  and  their  control  has  been  carefully  worked  out.  For- 
tunately, investigations  carried  out  in  1923  and  1924  by  Dr.  J.  L. 
Weimar  of  the  U.  S.  Department  of  Agriculture,  in  cooperation  with 
the  Farm  Advisors  of  Stanislaus,  Merced,  Los  Angeles,  and  Orange 
counties,  demonstrated  that  the  same  control  measures  that  have  proved 
so  effective  in  the  eastern  states  will  also  control  these  diseases  in 
California.  The  chief  diseases  are  briefly  described  below  and  on  the 
last  page  is  given  a  summary  of  the  methods  of  control. 

Black  Rot. — This  disease  is  caused  by  a  fungus  which  attacks  the 
underground  part  of  the  stem  as  well  as  the  potatoes.  Decayed  spots 
of  varying  size  appear  upon  the  potatoes.  These  spots  are  black  on 
the  surface  and  somewhat  sunken.  The  decay  often  starts  in  growth 
cracks  or  in  places  wounded  by  gophers;  while  in  storage,  cuts  and 
bruises  are  the  chief  starting  points.  The  decay  is  not  very  deep  and 
if  cut  away  the  sound  flesh  below  turns  a  greenish  color  soon  after 


ClRC.  285]  SWEET   POTATO   PRODUCTION    IN    CALIFORNIA 


21 


Fig.  8. — Selecting  seed  from  cull-pile  in  the  field.     The  wrong  way  to 

get  healthy  seed. 


-The  right  way  to  select  seed  sweet  potatoes.     The  hills  are  laid 
out  and  stem  of  each  one  is  examined  for  disease. 


22  UNIVERSITY    OF    CALIFORNIA EXPERIMENT   STATION 

exposure  to  air.  The  flesh  just  below  the  decayed  spots  is  very  bitter 
and  when  potatoes  affected  with  black  rot  are  cooked  the  bitterness 
permeates  the  whole  potato.  This  disease  is  often  found  on  seed  stock 
in  the  spring  as  black  patches  on  the  sides,  or  as  a  dry,  shriveled  and 
blackened  condition  at  the  stem  end  of  the  potato.  On  the  plant,  infec- 
tion by  Black  Rot  may  be  first  noted  at  the  time  the  plants  are  pulled 
in  the  hotbed  for  transplanting.  At  this  stage  the  stem  is  black  and 
decayed  for  a  short  distance  from  its  basal  end.  Such  plants  die  soon 
if  transplanted  to  the  field,  although  sometimes  when  conditions  are  not 
favorable  for  the  development  of  the  disease,  they  may  grow  and 
produce  several  potatoes  which  are  likely  to  be  diseased.    Many  plants 


Fig.  10. — Black  rot  on  sweet  potato,  showing  surface  decay.    (U.S.D.A.) 

that  do  not  show  infection  when  pulled  for  transplanting  may  really 
be  infected  and  die  after  transplanting.  Infected  plants  which  do  not 
die  in  the  early  part  of  the  season,  may  be  recognized  at  harvest  time 
by  the  dry  black  decay  of  the  lower  part  of  the  central  stem.  Such 
plants  usually  produce  only  a  few  small  potatoes. 

The  black  rot  fungus  attacks  no  plant  but  sweet  potatoes,  yet  it 
may  survive  in  the  soil  over  winter  and  even  for  several  years.  Rota- 
tion of  crops  is  therefore  a  necessity  as  a  part  of  any  method  of  control. 
But  if  the  soil  is  free  from  disease  to  begin  with  and  all  the  other 
measures  to  prevent  infection  are  observed,  several  crops  of  sweet 
potatoes  may  be  grown  in  succession  on  the  same  land.  The  most 
important  cause  of  infection  is  the  use  of  infected  seed.  If  potatoes 
showing  black  rot  are  bedded  in  the  plant  .bed,  the  fungus  grows 
from  the  mother  potato  and  attacks  the  new  plants.  Even  seed 
potatoes  that  appear  to  be  healthy,  generally  have  a  plentiful  supply 
of  the  fungus  on  their  surface,  if  they  have  been  stored  in  bins  with 


Circ.  285] 


SWEET   POTATO   PRODUCTION    IN    CALIFORNIA 


23 


infected  potatoes.  However,  healthy  plants  may  be  grown  from  seed 
of  this  kind  if  it  is  disinfected  before  bedding  according  to  the  direc- 
tions given  on  page  8,  and  bedded  in  a  disease-free  hotbed.  The  seed 
potatoes  that  have  visible  signs  of  Black  Rot  should  be  sorted  out  at 
bedding  time  and  destroyed  as  they  cannot  be  disinfected. 

Another  source  of  infection  is  the  soil  of  the  plant  bed.  On  many 
farms  there  is  only  one  spot  that  is  sunny,  sheltered  from  wind  and 
accessible  to  water.  The  tendency  is  to  make  the  sweet  potato  plant 
bed  in  this  one  favored  spot  year  after  year.     When  plant  pulling  is 


Fig.  11. — Black  rot  on  sweet  potato  plants,  upon  removal  from  hotbed. 

(U.SJD.A.) 


finished  in  the  spring,  the  old  beds  are  left  without  further  attention 
until  bedding  time  the  next  spring.  By  this  time  the  soil  in  and  around 
the  beds  is  likely  to  be  saturated  with  the  fungous  organisms  that 
cause  black  rot  and  other  diseases,  which  have  spread  from  the  decay- 
ing seed  potatoes  of  the  previous  year.  In  fact,  many  growers  prefer 
to  make  their  plant  beds  on  the  same  spot  as  in  previous  years  because 
of  the  improvement  in  physical  texture  of  the  soil  through  the  incor- 
poration of  the  decayed  seed,  plants  and  manure  of  previous  years. 
The  result  is  a  plant  bed  soil  thoroughly  infected  with  diseases  which 
infects  each  new  crop  of  plants  in  turn.  There  are  three  remedies  for 
this  situation.  One  is  to  make  the  plant  beds  in  a  fresh  spot  each 
year — but  this  is  not  always  possible.    Another  is  to  sterilize  the  soil 


24  UNIVERSITY    OF    CALIFORNIA EXPERIMENT   STATION 

before  preparing  the  plant  bed  each  spring.  Drenching  the  soil  with  a 
solution  of  formaldehyde  (one  pint  to  30  gallons  of  water)  at  the  rate 
of  one  gallon  to  each  square  foot  of  surface  would  probably  disinfect 
old  hotbed  soils  so  that  they  could  be  used  again.  Generally,  however, 
the  most  /practical  method  is  to  make  the  plant  bed  with  fresh  soil  or 
sand  hauled  from  a  place  where  contamination  by  sweet  potato  disease 
is  not  likely,  such  as  a  dry  creek  bed.  With  a  layer  of  this  soil  or 
sand  3  or  4  inches  deep  below  the  seed  potatoes,  and  a  covering  of  the 
same  material,  the  chances  of  infection  reaching  the  plants  from  with- 
out are  slight. 

Stem  Rot. — This  disease,  like  black  rot,  is  caused  by  a  fungus  that 
may  live  in  the  soil  for  several  years.  It  attacks  both  the  potatoes  and 
the  stems,  but  differs  from  black  rot  in  that  it  develops  entirely  within 
the  tissues,  being  seldom  visible  from  the  exterior  until  the  plant  dies. 
Potatoes  borne  by  diseased  plants  usually  contain  the  disease,  and  as 
they  are  likely  to  be  small  and  therefore  used  for  seed  purposes,  they 
are  one  of  the  chief  causes  of  the  spread  of  the  disease  from  year  to 
year.  In  advanced  stages,  potatoes  affected  with  stem  rot  show  a 
blackened  ring  just  below  the  skin,  but  so  many  in  less  advanced 
stages  do  not  show  this  ring  that  healthy  seed  cannot  be  secured  by 
discarding  those  that  do  not  show  this  discoloration.  The  only  way  to 
secure  absolutely  healthy  seed  is  to  select  them  from  healthy  plants  at 
digging  time.  Each  hill  should  be  inspected  by  splitting  the  central 
stem.  If  the  interior  is  brownish  in  color,  the  plant  is  infected  with 
stem  rot,  and  the  potatoes  it  bears  are  not  suitable  for  seed.  This 
disease  also  occurs  on  the  young  plants  in  the  hotbed,  the  leaves  becom- 
ing yellowish  and  the  underground  part  of  the  stem  bluish  in  color. 
These  plants  generally  die  before  or  soon  after  transplanting.  One 
of  the  commonest  causes  of  poor  stands  in  the  fields  is  the  early  death 
of  a  large  number  of  plants  that  became  diseased  in  the  hotbed.  When 
the  soil  of  the  field  contains  this  disease  more  plants  become  infected 
during  the  growing  season.  Such  plants  are  distinguished  by  their 
yellowish  or  brown  leaves,  and  by  the  blackened  dead  vines.  They  often 
have  formed  several  potatoes,  and  after  the  disease  kills  the  central 
stem  these  potatoes  send  up  sprouts  similar  to  those  ordinarily  pro- 
duced in  the  hotbed.  The  typical  appearance  of  plants  thus  affected  is 
shown  in  fig.  13.  Other  plants  affected  still  later  may  show  no  sign 
of  disease  until  the  stems  are  split  during  seed  inspection  at  digging 
time. 


Cmc.  285]  SWEET   POTATO   PRODUCTION    IN    CALIFORNIA 


25 


B 


Fig.  12. — Stem  rot  of  sweet  potato,  showing  the  discoloration  of 
vascular  tissue.     (U.S.D.A.) 


Fig.  13. — Stem  rot  often  affects  plants  as  shown  in  the  center — the  vines 
have  died  and  sprouts  have  grown  out  from  the  little  potatoes  already  formed. 


26 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


'■-<, 


Fig.  14. — Soft  rot,  showing  the  luxuriant  growth  of  the  fungus  on  the 
surface,  which  often  occurs  in  storage.     (U.S.D.A.) 


Cmc.285] 


SWEET   POTATO   PRODUCTION    IN    CALIFORNIA 


27 


Scurf. — This  disease  is  caused  by  a  fungus  that  occurs  in  many 
soils,  even  where  sweet  potatoes  have  never  been  grown.  It  is  most 
likely  to  affect  potatoes  on  soils  which  are  heavy  or  very  moist.  It 
causes  small  black  spots  on  the  skin  which  in  severe  cases  run  together, 
giving  the  potatoes  a  splotched  or  stained  appearance.  These  diseased 
areas  are  superficial,  seldom  extending  deeper  than  the  skin,  and  doing 
no  damage  aside  from  producing  their  unsightly  appearance.  The 
disease  is  prevented  to  a  large  extent  by  the  same  methods  as  those 
given  for  black  rot. 


Fig.  15. — King  rot  of  sweet  potato — caused  by  same  fungus  as  soft  rot. 

(U.S.D.A.) 


Soft  Rot. — This  disease  occurs  to  a  small  extent  in  the  field,  but 
does  its  main  damage  during  storage.  It  is  caused  by  one  of  the  most 
common  molds,  spores  of  which  are  in  the  soil  and  floating  in  the  air 
everywhere.  Fortunately,  this  mold  is  unable  to  penetrate  the  normal 
healthy  skin,  being  able  to  enter  the  potato  only  through  cuts  and 
bruises.  Hence,  careful  handling  of  storage  stock  lessens  the  chances 
of  decay.  Curing  the  sweet  potatoes  in  warm  dry  houses  just  after 
digging  increases  their  resistance  to  this  decay,  while  cold,  damp 
storage,  as  well  as  handling  or  sorting  while  in  storage,  greatly 
increases  the  chances  of  its  occurrence.  The  same  organism  often 
produces  a  dry  brownish  decay  known  as  ring  rot.     This  usually 


28  UNIVERSITY    OF    CALIFORNIA EXPERIMENT   STATION 

affects  only  portions  of  the  tuber  while  soft  rot  renders  the  whole 
tuber  mushy. 

Nematodes. — Nematode  injury,  usually  called  root  knot,  occurs  on 
sweet  potatoes  to  some  extent,  but  the  injury  to  this  crop  is  not  so 
severe  as  it  is  to  tomatoes,  melons,  and  other  garden  vegetables.  In 
fact,  very  satisfactory  crops  of  sweet  potatoes  can  be  grown  on  soils 
so  thoroughly  infested  with  nematodes  that  it  is  impossible  to  grow 
most  of  the  common  vegetables  and  fruits.  Nematode  injury  appears 
as  small  galls  on  the  fibrous  roots  of  the  sweet  potato  plant,  and  as 
larger  galls  on  the  root  end  of  the  potatoes.  Nematodes  are  easily 
spread  from  place  to  place  by  sweet  potato  plants;  therefore,  unless 
one  is  absolutely  sure  that  the  plants  are  free  of  nematodes,  sweet 
potatoes  should  not  be  grown  in  young  orchards  on  sandy  land  where 
nematode  infestation  would  have  serious  and  permanent  results. 
Nematodes  are  most  serious  on  light  sandy  soils.  It  is  said  that  they 
can  be  starved  out  by  growing  crops  immune  to  nematodes  for  two 
years.  All  cereal  crops  and  the  Iron. and  Brabham  varieties  of  cow 
peas  are  immune. 


THE  DISEASE   CONTEOL  PEOGEAMME 

The  grower  of  sweet  potatoes  when  once  he  realizes  the  losses  caused 
by  the  common  diseases,  will  wish  to  control  not  only  one,  but  all  of 
them,  especially  as  he  may  not  know  which  one  of  the  diseases  is  doing 
the  damage.  Fortunately,  the  control  of  each  of  the  common  diseases 
requires  practically  the  same  treatments.  No  one  treatment  will  be 
effective  against  any  disease,  hence,  it  is  necessary  to  follow  a  pro- 
gramme of  several  distinct  steps. 

1.  In  the  fall,  healthy  seed  should  be  selected  from  healthy  plants. 
The  stems  of  the  plants  are  split  at  digging  time,  and  seed  saved  only 
from  plants  that  show  no  internal  discoloration.  This  selected  seed 
should  be  kept  separate  from  other  potatoes  in  storage  to  avoid  the 
possibility  of  infection.  It  should  be  stored  in  new  boxes,  or  in  old 
boxes  that  have  been  disinfected  with  bluestone  solution  (1  pound  to 
25  gallons  of  water). 

2.  Just  before  bedding  time  in  the  spring,  the  seed  stock  should 
be  sorted  over.  All  potatoes  showing  black  rot  or  other  decay  must 
be  discarded. 

3.  Make  the  hotbed  in  a  new  place  each  year  or  use  fresh  soil  or 
sand  in  preparing  it. 


CIRC.  285]  SWEET    POTATO    PRODUCTION    IN    CALIFORNIA  29 

4.  Do  not  let  decayed  potatoes  become  mixed  with  the  soil  or  the 
manure  used  in  making  the  hotbed,  and  do  not  leave  them  lying  about 
near  the  bed. 

5.  Disinfect  the  seed  before  bedding,  by  dipping  it  for  10  minutes 
in  a  solution  of  corrosive  sublimate  (  4  ounces  to  32  gallons  of  water). 
See  page  8  for  details. 

6.  Discard  all  plants  that  show  any  evidence  of  disease  when  pull- 
ing for  transplanting,  especially  those  showing  black  or  bluish  dis- 
coloration on  the  basal  portion  of  the  stem. 

7.  Grow  sweet  potatoes  wherever  possible  on  land  that  has  not  been 
used  for  this  crop  in  several  years. 

8.  Try  to  grow  healthy  seed  and  healthy  plants  at  home  rather 
than  buy  them  from  some  other  section  where  diseases  are  likely  to 
be  just  as  common. 


STATION  PUBLICATIONS  AVAILABLE  FOR  FREE  DISTRIBUTION 


BULLETINS 


No.  No. 

253.  Irrigation  and   Soil  Conditions  in  the  352. 

Sierra  Nevada  Foothills,  California. 

261.  Melaxuma    of    the    Walnut,    "Juglans  353. 

regia."  354. 

262.  Citrus  Diseases  of  Florida   and  Cuba  357. 

Compared  with  Those  of  California. 

263.  Size  Grades  for  Ripe  Olives. 

268.  Growing  and  Grafting  Olive  Seedlings.  358. 

273.   Preliminary  Report  on  Kearney  Vine- 
yard Experimental  Drain.  359. 

275.  The  Cultivation  of  Belladonna  in  Cali-  361. 

fornia. 

276.  The  Pomegranate.  362. 

277.  Sudan  Grass  363. 

278.  Grain  Sorghums. 

279.  Irrigation  of  Rice  in  California.  364. 

280.  Irrigation  of  Alfalfa  in  the  Sacramento 

Valley.  366. 

283.  The  Olive  Insects  of  California. 

285.  The  Milk  Goat  in  California.  367. 

286.  Commercial  Fertilizers. 

294.   Bean  Culture  in  California.  368. 

304.  A  Study  of  the  Effects  of  Freezes  on 

Citrus   in   California.  369. 

310.  Plum  Pollination.  370. 

312.  Mariout  Barley.  371. 

313.  Pruning  Young  Deciduous  Fruit  Trees. 

319.   Caprifigs  and  Caprification.  372. 

324.  Storage  of  Perishable  Fruit  at  Freezing 

Temperatures.  374. 

325.  Rice  Irrigation  Measurements  and  Ex- 

periments    in      Sacramento     Valley, 
1914-1919.  375. 

328.   Prune  Growing  in  California. 

331.   Phylloxera-Resistant  Stocks.  376. 

334.  Preliminary  Volume  Tables  for  Second- 

Growth  Redwood.  377. 

335.  Cocoanut   Meal    as    a    Feed   for   Dairy  379. 

Cows  and  Other  Livestock.  380. 

339.  The  Relative  Cost  of  Making  Logs  from 

Small  and  Large  Timber.  381. 

340.  Control  of  the  Pocket  Gopher  in  Cali- 

fornia. 382. 

343.  Cheese  Pests  and  Their  Control. 

344.  Cold  Storage  as  an  Aid  to  the  Market-  383. 

ing  of  Plums. 

346.  Almond  Pollination.  384. 

347.  The  Control  of  Red  Spiders  in  Decidu- 

ous Orchards. 

348.  Pruning  Young  Olive  Trees.  385. 

349.  A    Study    of    Sidedraft    and    Tractor  386. 

Hitches. 

350.  Agriculture  in  Cut-over  Redwood  Lands.  387. 


Further  Experiments  in  Plum  Pollina- 
tion. 

Bovine  Infectious  Abortion. 

Results  of  Rice  Experiments  in  1922. 

A  Self-mixing  Dusting  Machine  for 
Applying  Dry  Insecticides  and 
Fungicides. 

Black  Measles,  Water  Berries,  and 
Related  Vine  Troubles. 

Fruit  Beverage  Investigations. 

Preliminary  Yield  Tables  for  Second 
Growth  Redwood. 

Dust  and  the  Tractor  Engine. 

The  Pruning  of  Citrus  Trees  in  Cali- 
fornia. 

Fungicidal  Dusts  for  the  Control  of 
Bunt. 

Turkish  Tobacco  Culture,  Curing  and 
Marketing. 

Methods  of  Harvesting  and  Irrigation 
in  Relation  to  Mouldy  Walnuts. 

Bacterial  Decomposition  of  Olives  dur- 
ing Pickling. 

Comparison  of  Woods  for  Butter  Boxes. 

Browning  of  Yellow  Newtown  Apples. 

The  Relative  Cost  of  Yarding  Small 
and  Large  Timber. 

The  Cost  of  Producing  Market  Milk  and 
Butterfat  on  246  California  Dairies. 

A  Survey  of  Orchard  Practices  in  the 
Citrus  Industry  of  Southern  Cali- 
fornia. 

Results  of  Rice  Experiments  at  Cor- 
tena,   1923. 

Sun-Drying  and  Dehydration  of  Wal- 
nuts. 

The  Cold  Storage  of  Pears. 

Walnut  Culture  in  California. 

Growth  of  Eucalyptus  in  California 
Plantations. 

Growing  and  Handling  Asparagus 
Crowns. 

Pumping  for  Drainage  in  the  San 
Joaquin  Valley,   California. 

Monilia  Blossom  Blight  (Brown  Rot) 
of  Apricot. 

A  Study  of  the  Relative  Values  of  Cer- 
tain Succulent  Feeds  and  Alfalfa  Meal 
as  Sourses  of  Vitamin  A  for  Poultry. 

Pollination  of  the  Sweet  Cherry. 

Pruning  Bearing  Deciduous  Fruit 
Trees. 

Fig  Smut. 


CIRCULARS 


No. 


Alfalfa. 

Correspondence  Courses  in  Agriculture. 

The    Selection    and    Cost   of    a    Small 
Pumping  Plant. 

House  Fumigation. 

The  Control  of  Citrus  Insects. 
136.  Melilotus    indica    as    a    Green-Manure 
Crop  for  California. 

Oidium  or  Powdery  Mildew  of  the  Vine. 

Feeding  and  Management  of  Hogs. 

Some  Observations  on  the  Bulk  Hand- 
ling of  Grain  in  California. 

Irrigation  Practice  in  Growing  Small 
Fruit  in  California. 


87. 
113. 
117. 

127. 
129. 


144. 
151. 
152. 

154. 


No. 

155.  Bovine  Tuberculosis. 

157.  Control  of  the  Pear  Scab. 

160.  Lettuce  Growing  in  California. 

161.  Potatoes  in  California. 

164.  Small  Fruit  Culture  in  California. 

165.  Fundamentals   of   Sugar   Beet   Culture 

under  California  Conditions. 

166.  The  County  Farm  Bureau. 

167.  Feeding  Stuffs  of  Minor  Importance. 
170.   Fertilizing  California  Soils  for  the  1918 

Crop. 
173.  The    Construction    of   the   Wood-Hoop 

Silo. 
178.  The  Packing  of  Apples  in  California. 


CIRCULARS — (Continued) 


No. 

179.   Factors    of    Importance    in    Producing 

Milk  of  Low  Bacterial  Count. 
184.  A  Flock  of  Sheep  on  the  Farm. 
190.  Agriculture  Clubs  in  California. 
199.  Onion  Growing  in  California. 

202.  County   Organizations   for   Rural   Fire 

Control. 

203.  Peat  as  a  Manure  Substitute. 

208.  Summary  of  the  Annual  Reports  of  the 

Farm  Advisors  of  California. 

209.  The  Function  of  the  Farm  Bureau.  _ 

210.  Suggestions 'to  the  Settler  in  California. 
212.   Salvaging  Rain-Damaged  Prunes. 

214.  Seed  Treatment  for  the  Prevention  of 

Cereal  Smuts. 

215.  Feeding  Dairy  Cows  in  California. 
217.  Methods   for   Marketing  Vegetables   in 

California. 
220.   Unfermented  Fruit  Juices. 
228.   Vineyard  Irrigation  in  Arid  Climates. 

231.  The  Home  Vineyard. 

232.  Harvesting    and    Handling    California 

Cherries  for  Eastern   Shipment. 

233.  Artificial  Incubation. 

234.  Winter  Injury  to  Young  Walnut  Trees 

during  1921-22. 

235.  Soil  Analysis  and  Soil  and  Plant  Inter- 
relations. 

236.  The  Common  Hawks  and  Owls  of  Cali- 

fornia   from   the    Standpoint   of   the 
Rancher. 

237.  Directions  for  the  Tanning  and  Dress- 

of  Furs. 

238.  The  Apricot  in  California. 

239.  Harvesting  and  Handling  Apricots  and 

Plums  for  Eastern  Shipment. 

240.  Harvesting    and    Handling    Pears   for 

Eastern  Shipment. 

241.  Harvesting  and  Handling  Peaches  for 

Eastern   Shipment. 

243.  Marmalade  Juice  and  Jelly  Juice  from 

Citrus  Fruits. 

244.  Central  Wire  Bracing  for  Fruit  Trees. 

245.  Vine  Pruning  Systems. 

247.  Colonization  and  Rural  Development. 

248.  Some  Common  Errors  in  Vine  Pruning 

and  Their  Remedies. 

249.  Replacing  Missing  Vines. 

250.  Measurement   of    Irrigation   Water   on 

the  Farm. 


No. 

251.  Recommendations  Concerning  the  Com- 

mon    Diseases     and     Parasites     of 
Poultry  in  California. 

252.  Supports  for  Vines. 

253.  Vineyard  Plans. 

254.  The  Use  of  Artificial  Light  to  Increase 

Winter  Egg  Production. 

255.  Leguminous  Plants  as  Organic  Fertil- 

izer in  California  Agriculture. 

256.  The  Control  of  Wild  Morning  Glory. 

257.  The  Small-Seeded  Horse  Bean. 

258.  Thinning  Deciduous  Fruits. 

259.  Pear  By-products. 

260.  A  Selected  List  of  References  Relating 

to  Irrigation  in  California. 

261.  Sewing  Grain   Sacks. 

262.  Cabbage  Growing  in  California. 

263.  Tomato  Production  in  California. 

264.  Preliminary  Essentials  to  Bovine  Tuber- 

culosis Control. 

265.  Plant  Disease  and  Pest  Control. 

266.  Analyzing  the  Citrus  Orchard  by  Means 

of  Simple  Tree  Records. 

267.  The  Tendency  of  Tractors  to  Rise  in 

Front;  Causes  and  Remedies. 

268.  Inexpensive  Lavor-saving  Poultry  Ap- 

pliances. 

269.  An  Orchard  Brush  Burner. 

270.  A  Farm  Septic  Tank. 

271.  Brooding  Chicks  Artificially. 

272.  California  Farm  Tenancy  and  Methods 

of  Leasing. 

273.  Saving  the  Gophered  Citrus  Tree. 

275.  Marketable        California        Decorative 

Greens. 

276.  Home  Canning. 

277.  Head,   Cane,   and  Cordon   Pruning  of 

Vines. 

278.  Olive  Pickling  in  Mediterranean  Coun- 

tries. 

279.  The  Preparation  and  Refining  of  Olive 

Oil  in  Southern  Europe. 

281.  The  Results  of  a  Survey  to  Determine 

the  Cost  of  Producing  Beef  in  Cali- 
fornia. 

282.  Prevention  of  Insect  Attack  on  Stored 

Grain. 

283.  Fertilizing  Citrus  Trees  in  California. 

284.  The  Almond  in  California. 


The  publications  listed  above  may  be  had  by  addressing 

College  of  Agriculture, 

University  of  California, 

Berkeley,  California. 


12m-5,'25 


